Viability: Can confirm its playable from start to end! I beat the boss!
Presentation: The rules and controls are undertandable but I think adding them to your start screen would be ideal in the final build.
Theme: The description of the game helps me undertand what you're going for as well as the general layout of a platformer, but I would love to see art to go along with this concept. It may also allow others not as familiar as game dev to understand what you're going for. The current build did fuel my imagination though, if you are low on time perhaps you could see how abstract you could make it without details...? because I understood the idea with just shapes. I do hope you get to add art tailored to the style you're going for though. Your concept gives you fun options!
Engagement: As mentioned earlier, the game did capture my imagination! I think with art it will be even more exciting! I did enjoy playing, although the default playground parkour physics do feel a bit too slide-y and sensitive to me. Perhaps adjusting the movement to be a bit less sensitive would be a good idea if possible?
As for the boss, it suprised me at first (in a good way). I wasn't expecting a bullet hell level! I quickly got used to their attacks and timing. I think this happens quite a bit for bosses in games in general but I think diverse attacks and catching the player off-guard would make it more exciting! I actually think the bullets should have multiple randomized attacks if possible, one can be the staggered pattern and then maybe the boss fires them all at the same time as a suprise attack?
I do wonder... What happens when you die to the boss? Where do you restart? I wouldn't be too harsh with that personally. I'd have the player restart on the boss level if they die. I'd also possibly consider health pickups in the boss arena if you choose to adjust boss difficulty.
Overall one fun, complete level or two with a story! Would love to see where this goes! -Luke